On any given day, they'll respond to about 25 calls in a 24-hour period.

The firefighters love putting out fires. But what makes Engine Company 10 so very busy is this: The vast majority of the 7,000-plus calls the firefighters answer each year are not fires at all. They are, in fact, medical calls.

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Sound the Alarm

"Nightline" followed the department over many shifts and several days. Many medical calls came in. A woman, combative and running into the street, was thought to be on the drug PCP. A 50-year-old man hemorrhaging blood because of -- he says -- a mistake in his routine kidney dialysis treatment. An 82-year-old woman bleeding from her rectal area. An 83-year-old with respiratory distress.

Leo Ruiz is a paramedic firefighter with Engine Company 10. He has all the training and skill of an Army battlefield medic. Like many of his fellow firefighters, he loves serving his community.

But he signed up to fight fires. And as we followed Engine 10, we saw it happen again and again. When the men at Engine 10 arrive on the scene of a call, it's not a fire hose they pull out; it's a medical bag.

Firefighters in 'Vortex of Sickness'

The engine company serves a neighborhood called Trinidad, where most people are poor and don't have good access to doctors. They get sick and they call 911. Emergency operators then call in Engine 10.

The firefighters call the community they serve "the vortex of sickness."

"It's an area where we run a lot of sick people," said firefighter JR Muyleart. "A whole lot. If they drank more of this," he laughed, holding up an orange juice container, "they'd cut down on health care costs."

"Vortex of sickness" is a name that reflects both the real medical needs of the area and a certain level of frustration among the firefighters.

Ruiz described one call as it was happening.

"We're going for a 20-year old-female with a headache," said Ruiz. "Most of the time, it is [minor]."

That's not to say these firefighters don't get their fair share of real medical emergencies. On one call they found a 24-year-old man in full diabetic coma, unconscious on a couch.

"We're gonna go ahead and help him out, OK?" said Ruiz. "What we'll do is we'll start an IV."

It's not the first time this particular patient has called 911.

"This ever happen to you before, that your sugar dropped low?" Ruiz asked the patient, who told him it happens "all the time." "When's the last time that happened?" Ruiz asked. The patient explained that it happened so frequently he couldn't think of the last time.

"Do you want to go to the hospital with us today?"

The patient said no.

But just minutes after returning from reviving that man from a diabetic coma, they had to go back. He thought they had stolen some of his money.

"He thought he lost money. So he called the ambulance," said Ruiz.

Muyleart explained: "So on that call, that's a diabetic that we just ran to help, who was in a diabetic coma when we got there. And he thought he had some money, and apparently he thought we stole his money, so he called 911 back. ... That's what you call 911 abuse."

At times, some of the firefighters can't help feeling that some residents -- particularly those who dial 911 again and again -- are somehow gaming the system.

The routine of medical calls can be grueling, they say. If it was up to many of these men, they'd fight fires all day, every day.

"Definitely fires," Muyleart said.

Firefighters: How Much Does That Cost?

Consider the numbers: It costs taxpayers about $3,500 every time Engine 10 leaves the station. That's about $3,500, 25 times a day, just for this one company.

But according to Washington D.C. Fire and Emergency Medical Services Chief Dennis Rubin, the system is necessary and effective.

"It does drain the system, it does cost taxpayer money," said Rubin. But, he said, "I can't say no to [residents]."

"I think in any community that has a poor area, less advantaged than others, the service of the fire department, whether it's medical or fire responses, always seems to be on an uptick," Rubin continued. "Also we have a large homeless population in this area and on top of that we have an aging population."

The chief said most firefighters embrace their work, whatever it brings.

"I think they're here to help people," Rubin said. "And I really believe that in my mind, in my heart, in my spirit. I think they put on the badge and I think they've sworn to protect the people no matter what it is."

Making the rounds with Engine Company 10, it becomes clear that there is a huge gap in meeting the medical needs of this community -- and perhaps the community has found a way to fill that gap themselves.

"When you look at the poor people, no one else is taking on those responsibilities," said Rubin. "No one else is doing it."

The firefighters can see it from the residents' side, too.

"I think I guess my personal feeling on it is that maybe it's sort of something that's been ingrained in the culture of the neighborhood here," said Ruiz. "You're sick, you call 911. It doesn't matter what it is, you always have an ambulance that will come, the fire department will always respond and they'll take you to the hospital."

Moments of Frustration

It does wear on the men. There are moments of real frustration.

On one call the firefighters encountered a drunk man in the street with multiple wristbands from hospital stays. He was moaning loudly and moving erratically.

They took his blood pressure. Then they put the patient on a stretcher and took him to the hospital, where for at least one more night he'd be warm, safe and fed.

Back at the firehouse, we asked whether the patient had really been having any kind of medical emergency at all.

"Well, he had a tag on from today and yesterday," said Richard Sheltra, another firefighter. "So he went every day to get something to eat and to stay for the night. And he'll be released in the morning and will do the same routine tomorrow.

Muyleart explained that like so many of their patients, "I've seen him before. He hangs out in that exact same spot."

The hospital has to take the patient, Muyleart said.

"Oh yeah, they have to. Just like we have to transport them."

Because that's the system. And the interesting thing about the House of Pain is, firefighters line up to get assigned here. Those who get in are like a family who will do the medical runs because they have to.

But when a call comes in like the one that came at 11 p.m. the other night -- an honest-to-goodness fire -- the engine company really snapped to. This time, there was a fire to put out, the job they do because they love to.